This invention relates to stent carrying balloon catheters, sometimes referred to as dilatation catheters, for use in angioplasty and other various vessel repair procedures. Angioplasty has become recognized as an efficient and effective method of opening stenoses in the vascular system. In the most widely used form of angioplasty, a balloon catheter is guided through the vascular system until the balloon, which is carried at the distal end of a catheter shaft, and which may carry an expandable stent, is positioned across the stenosis or lesion, i.e., vessel obstruction. The balloon is then inflated to apply pressure to the obstruction which is essentially re molded by pressing it against the inner wall of the vessel whereby the vessel is opened for improved flow. Due the expansion of the balloon, the stent, which is situated on the balloon, is also expanded and released to aid in support and/or repair of the vessel wall.
Balloon catheters are of various types. One type is fed over a guide wire (i.e., “over-the-wire” catheters) and another type serves as its own guide wire (i.e., “fixed-wire” catheters). Variations of these two basic types also have been developed such as the so called “rapid exchange” type, “innerless” catheters, and others. As used herein, the term “balloon catheter” is meant to include all of the various types of angioplasty catheters which carry a balloon for performing angioplasty and any other type of stent carrying balloon catheter. Balloon catheters may also be of a wide variety of inner structure, such as different lumen design, of which there are at least three basic types: triple lumen, dual lumen and co-axial lumen. All varieties of internal structure and design variation are meant to be included by use of the term “balloon catheter” herein.
When used in percutaneous transluminal coronary angioplasty (PTCA), the balloon catheter is typically advanced through a guide catheter to a preselected vessel location, such as the aorta, for example. Using fluoroscopy, the surgeon manipulates the catheter until the balloon is located across the stenosis or obstruction. As already pointed out, this may involve the use of a guide wire over which the catheter is moved or alternatively the catheter may act as its own guide wire, depending on the particular design. The manipulation of the stent carrying balloon catheter through the guide catheter and through the vessels to the obstruction requires the balloon catheter to have a number of different features.
One such feature is the use of a lubricious coating over the exterior surfaces of the catheter and balloon to facilitate movement of the catheter through the sometimes tortuous paths within the vascular system to the preselected vessel location for performing the angioplasty. A wide variety of such lubricious coatings have become commonplace for use with respect to catheters and other devices which are insertable into the body in connection with surgical procedures and the like. All such coatings are intended to be included herein with respect to the use of the term “lubricious coating”. Examples of such coatings include silicone and most preferably hydrophilic coatings involving hydrogel polymers or the like, such as polymer networks of a vinyl polymer and an uncrosslinked hydrogel, for example. Polyethylene oxide (PEO) is a preferred hydrogel. A preferred vinyl polymer is neopentyl glycol diacrylate (NPG). Such compositions are more fully disclosed in co-pending U.S. patent application Ser. No. 07/809,889 which is assigned to the same assignee as is the present invention and which is incorporated herein by reference.
These coatings have even been known to include certain agents such as drugs which may be permanently entrapped in the coating or leachable therefrom into the body. For example, heparin has been used in such a fashion. Heparin is well known as an agent which is often used to inhibit clot formation in the blood. Again, the term “lubricious coating” is meant to include all such variations.
One problem with a stent carrying balloon catheter having a lubricious coating is that during location and release of the carried stent, the stent tends to slip off the balloon due to the lubricious coating on the balloon. Coating both the shaft and balloon of the catheter inhibits the doctor's ability to locate, activate and deploy stents at any particular lesion. The stent is sometimes worked off the balloon portion during the insertion of the catheter and during the expansion of the balloon. This unexpected movement of the stent might be regarded negatively by a surge on. The present invention provides for more se cure connection between the balloon and the stent to prevent such slippage. Thus, though high lubricity is desirable for general movement, it is also desirable to provide a means of anchoring or positioning the stent in a fixed location on the balloon so as to avoid unexpected movement thereof upon the balloon during positioning and expansion.